1// class template regex -*- C++ -*-
2
3// Copyright (C) 2013-2018 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/**
26 * @file bits/regex_executor.tcc
27 * This is an internal header file, included by other library headers.
28 * Do not attempt to use it directly. @headername{regex}
29 */
30
31namespace std _GLIBCXX_VISIBILITY(default)
32{
33_GLIBCXX_BEGIN_NAMESPACE_VERSION
34
35namespace __detail
36{
37 template<typename _BiIter, typename _Alloc, typename _TraitsT,
38 bool __dfs_mode>
39 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
40 _M_search()
41 {
42 if (_M_search_from_first())
43 return true;
44 if (_M_flags & regex_constants::match_continuous)
45 return false;
46 _M_flags |= regex_constants::match_prev_avail;
47 while (_M_begin != _M_end)
48 {
49 ++_M_begin;
50 if (_M_search_from_first())
51 return true;
52 }
53 return false;
54 }
55
56 // The _M_main function operates in different modes, DFS mode or BFS mode,
57 // indicated by template parameter __dfs_mode, and dispatches to one of the
58 // _M_main_dispatch overloads.
59 //
60 // ------------------------------------------------------------
61 //
62 // DFS mode:
63 //
64 // It applies a Depth-First-Search (aka backtracking) on given NFA and input
65 // string.
66 // At the very beginning the executor stands in the start state, then it
67 // tries every possible state transition in current state recursively. Some
68 // state transitions consume input string, say, a single-char-matcher or a
69 // back-reference matcher; some don't, like assertion or other anchor nodes.
70 // When the input is exhausted and/or the current state is an accepting
71 // state, the whole executor returns true.
72 //
73 // TODO: This approach is exponentially slow for certain input.
74 // Try to compile the NFA to a DFA.
75 //
76 // Time complexity: \Omega(match_length), O(2^(_M_nfa.size()))
77 // Space complexity: \theta(match_results.size() + match_length)
78 //
79 template<typename _BiIter, typename _Alloc, typename _TraitsT,
80 bool __dfs_mode>
81 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
82 _M_main_dispatch(_Match_mode __match_mode, __dfs)
83 {
84 _M_has_sol = false;
85 *_M_states._M_get_sol_pos() = _BiIter();
86 _M_cur_results = _M_results;
87 _M_dfs(__match_mode, _M_states._M_start);
88 return _M_has_sol;
89 }
90
91 // ------------------------------------------------------------
92 //
93 // BFS mode:
94 //
95 // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html)
96 // explained this algorithm clearly.
97 //
98 // It first computes epsilon closure (states that can be achieved without
99 // consuming characters) for every state that's still matching,
100 // using the same DFS algorithm, but doesn't re-enter states (using
101 // _M_states._M_visited to check), nor follow _S_opcode_match.
102 //
103 // Then apply DFS using every _S_opcode_match (in _M_states._M_match_queue)
104 // as the start state.
105 //
106 // It significantly reduces potential duplicate states, so has a better
107 // upper bound; but it requires more overhead.
108 //
109 // Time complexity: \Omega(match_length * match_results.size())
110 // O(match_length * _M_nfa.size() * match_results.size())
111 // Space complexity: \Omega(_M_nfa.size() + match_results.size())
112 // O(_M_nfa.size() * match_results.size())
113 template<typename _BiIter, typename _Alloc, typename _TraitsT,
114 bool __dfs_mode>
115 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
116 _M_main_dispatch(_Match_mode __match_mode, __bfs)
117 {
118 _M_states._M_queue(_M_states._M_start, _M_results);
119 bool __ret = false;
120 while (1)
121 {
122 _M_has_sol = false;
123 if (_M_states._M_match_queue.empty())
124 break;
125 std::fill_n(_M_states._M_visited_states.get(), _M_nfa.size(), false);
126 auto __old_queue = std::move(_M_states._M_match_queue);
127 for (auto& __task : __old_queue)
128 {
129 _M_cur_results = std::move(__task.second);
130 _M_dfs(__match_mode, __task.first);
131 }
132 if (__match_mode == _Match_mode::_Prefix)
133 __ret |= _M_has_sol;
134 if (_M_current == _M_end)
135 break;
136 ++_M_current;
137 }
138 if (__match_mode == _Match_mode::_Exact)
139 __ret = _M_has_sol;
140 _M_states._M_match_queue.clear();
141 return __ret;
142 }
143
144 // Return whether now match the given sub-NFA.
145 template<typename _BiIter, typename _Alloc, typename _TraitsT,
146 bool __dfs_mode>
147 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
148 _M_lookahead(_StateIdT __next)
149 {
150 // Backreferences may refer to captured content.
151 // We may want to make this faster by not copying,
152 // but let's not be clever prematurely.
153 _ResultsVec __what(_M_cur_results);
154 _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags);
155 __sub._M_states._M_start = __next;
156 if (__sub._M_search_from_first())
157 {
158 for (size_t __i = 0; __i < __what.size(); __i++)
159 if (__what[__i].matched)
160 _M_cur_results[__i] = __what[__i];
161 return true;
162 }
163 return false;
164 }
165
166 // __rep_count records how many times (__rep_count.second)
167 // this node is visited under certain input iterator
168 // (__rep_count.first). This prevent the executor from entering
169 // infinite loop by refusing to continue when it's already been
170 // visited more than twice. It's `twice` instead of `once` because
171 // we need to spare one more time for potential group capture.
172 template<typename _BiIter, typename _Alloc, typename _TraitsT,
173 bool __dfs_mode>
174 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
175 _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i)
176 {
177 const auto& __state = _M_nfa[__i];
178 auto& __rep_count = _M_rep_count[__i];
179 if (__rep_count.second == 0 || __rep_count.first != _M_current)
180 {
181 auto __back = __rep_count;
182 __rep_count.first = _M_current;
183 __rep_count.second = 1;
184 _M_dfs(__match_mode, __state._M_alt);
185 __rep_count = __back;
186 }
187 else
188 {
189 if (__rep_count.second < 2)
190 {
191 __rep_count.second++;
192 _M_dfs(__match_mode, __state._M_alt);
193 __rep_count.second--;
194 }
195 }
196 }
197
198 // _M_alt branch is "match once more", while _M_next is "get me out
199 // of this quantifier". Executing _M_next first or _M_alt first don't
200 // mean the same thing, and we need to choose the correct order under
201 // given greedy mode.
202 template<typename _BiIter, typename _Alloc, typename _TraitsT,
203 bool __dfs_mode>
204 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
205 _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i)
206 {
207 const auto& __state = _M_nfa[__i];
208
209 // Greedy.
210 if (!__state._M_neg)
211 {
212 _M_rep_once_more(__match_mode, __i);
213 // If it's DFS executor and already accepted, we're done.
214 if (!__dfs_mode || !_M_has_sol)
215 _M_dfs(__match_mode, __state._M_next);
216 }
217 else // Non-greedy mode
218 {
219 if (__dfs_mode)
220 {
221 // vice-versa.
222 _M_dfs(__match_mode, __state._M_next);
223 if (!_M_has_sol)
224 _M_rep_once_more(__match_mode, __i);
225 }
226 else
227 {
228 // DON'T attempt anything, because there's already another
229 // state with higher priority accepted. This state cannot
230 // be better by attempting its next node.
231 if (!_M_has_sol)
232 {
233 _M_dfs(__match_mode, __state._M_next);
234 // DON'T attempt anything if it's already accepted. An
235 // accepted state *must* be better than a solution that
236 // matches a non-greedy quantifier one more time.
237 if (!_M_has_sol)
238 _M_rep_once_more(__match_mode, __i);
239 }
240 }
241 }
242 }
243
244 template<typename _BiIter, typename _Alloc, typename _TraitsT,
245 bool __dfs_mode>
246 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
247 _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i)
248 {
249 const auto& __state = _M_nfa[__i];
250
251 auto& __res = _M_cur_results[__state._M_subexpr];
252 auto __back = __res.first;
253 __res.first = _M_current;
254 _M_dfs(__match_mode, __state._M_next);
255 __res.first = __back;
256 }
257
258 template<typename _BiIter, typename _Alloc, typename _TraitsT,
259 bool __dfs_mode>
260 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
261 _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i)
262 {
263 const auto& __state = _M_nfa[__i];
264
265 auto& __res = _M_cur_results[__state._M_subexpr];
266 auto __back = __res;
267 __res.second = _M_current;
268 __res.matched = true;
269 _M_dfs(__match_mode, __state._M_next);
270 __res = __back;
271 }
272
273 template<typename _BiIter, typename _Alloc, typename _TraitsT,
274 bool __dfs_mode>
275 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
276 _M_handle_line_begin_assertion(_Match_mode __match_mode, _StateIdT __i)
277 {
278 const auto& __state = _M_nfa[__i];
279 if (_M_at_begin())
280 _M_dfs(__match_mode, __state._M_next);
281 }
282
283 template<typename _BiIter, typename _Alloc, typename _TraitsT,
284 bool __dfs_mode>
285 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
286 _M_handle_line_end_assertion(_Match_mode __match_mode, _StateIdT __i)
287 {
288 const auto& __state = _M_nfa[__i];
289 if (_M_at_end())
290 _M_dfs(__match_mode, __state._M_next);
291 }
292
293 template<typename _BiIter, typename _Alloc, typename _TraitsT,
294 bool __dfs_mode>
295 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
296 _M_handle_word_boundary(_Match_mode __match_mode, _StateIdT __i)
297 {
298 const auto& __state = _M_nfa[__i];
299 if (_M_word_boundary() == !__state._M_neg)
300 _M_dfs(__match_mode, __state._M_next);
301 }
302
303 // Here __state._M_alt offers a single start node for a sub-NFA.
304 // We recursively invoke our algorithm to match the sub-NFA.
305 template<typename _BiIter, typename _Alloc, typename _TraitsT,
306 bool __dfs_mode>
307 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
308 _M_handle_subexpr_lookahead(_Match_mode __match_mode, _StateIdT __i)
309 {
310 const auto& __state = _M_nfa[__i];
311 if (_M_lookahead(__state._M_alt) == !__state._M_neg)
312 _M_dfs(__match_mode, __state._M_next);
313 }
314
315 template<typename _BiIter, typename _Alloc, typename _TraitsT,
316 bool __dfs_mode>
317 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
318 _M_handle_match(_Match_mode __match_mode, _StateIdT __i)
319 {
320 const auto& __state = _M_nfa[__i];
321
322 if (_M_current == _M_end)
323 return;
324 if (__dfs_mode)
325 {
326 if (__state._M_matches(*_M_current))
327 {
328 ++_M_current;
329 _M_dfs(__match_mode, __state._M_next);
330 --_M_current;
331 }
332 }
333 else
334 if (__state._M_matches(*_M_current))
335 _M_states._M_queue(__state._M_next, _M_cur_results);
336 }
337
338 template<typename _BiIter, typename _TraitsT>
339 struct _Backref_matcher
340 {
341 _Backref_matcher(bool __icase, const _TraitsT& __traits)
342 : _M_traits(__traits) { }
343
344 bool
345 _M_apply(_BiIter __expected_begin,
346 _BiIter __expected_end, _BiIter __actual_begin,
347 _BiIter __actual_end)
348 {
349 return _M_traits.transform(__expected_begin, __expected_end)
350 == _M_traits.transform(__actual_begin, __actual_end);
351 }
352
353 const _TraitsT& _M_traits;
354 };
355
356 template<typename _BiIter, typename _CharT>
357 struct _Backref_matcher<_BiIter, std::regex_traits<_CharT>>
358 {
359 using _TraitsT = std::regex_traits<_CharT>;
360 _Backref_matcher(bool __icase, const _TraitsT& __traits)
361 : _M_icase(__icase), _M_traits(__traits) { }
362
363 bool
364 _M_apply(_BiIter __expected_begin,
365 _BiIter __expected_end, _BiIter __actual_begin,
366 _BiIter __actual_end)
367 {
368 if (!_M_icase)
369 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
370 __actual_begin, __actual_end);
371 typedef std::ctype<_CharT> __ctype_type;
372 const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc());
373 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
374 __actual_begin, __actual_end,
375 [this, &__fctyp](_CharT __lhs, _CharT __rhs)
376 {
377 return __fctyp.tolower(__lhs)
378 == __fctyp.tolower(__rhs);
379 });
380 }
381
382 bool _M_icase;
383 const _TraitsT& _M_traits;
384 };
385
386 // First fetch the matched result from _M_cur_results as __submatch;
387 // then compare it with
388 // (_M_current, _M_current + (__submatch.second - __submatch.first)).
389 // If matched, keep going; else just return and try another state.
390 template<typename _BiIter, typename _Alloc, typename _TraitsT,
391 bool __dfs_mode>
392 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
393 _M_handle_backref(_Match_mode __match_mode, _StateIdT __i)
394 {
395 __glibcxx_assert(__dfs_mode);
396
397 const auto& __state = _M_nfa[__i];
398 auto& __submatch = _M_cur_results[__state._M_backref_index];
399 if (!__submatch.matched)
400 return;
401 auto __last = _M_current;
402 for (auto __tmp = __submatch.first;
403 __last != _M_end && __tmp != __submatch.second;
404 ++__tmp)
405 ++__last;
406 if (_Backref_matcher<_BiIter, _TraitsT>(
407 _M_re.flags() & regex_constants::icase,
408 _M_re._M_automaton->_M_traits)._M_apply(
409 __submatch.first, __submatch.second, _M_current, __last))
410 {
411 if (__last != _M_current)
412 {
413 auto __backup = _M_current;
414 _M_current = __last;
415 _M_dfs(__match_mode, __state._M_next);
416 _M_current = __backup;
417 }
418 else
419 _M_dfs(__match_mode, __state._M_next);
420 }
421 }
422
423 template<typename _BiIter, typename _Alloc, typename _TraitsT,
424 bool __dfs_mode>
425 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
426 _M_handle_accept(_Match_mode __match_mode, _StateIdT __i)
427 {
428 if (__dfs_mode)
429 {
430 __glibcxx_assert(!_M_has_sol);
431 if (__match_mode == _Match_mode::_Exact)
432 _M_has_sol = _M_current == _M_end;
433 else
434 _M_has_sol = true;
435 if (_M_current == _M_begin
436 && (_M_flags & regex_constants::match_not_null))
437 _M_has_sol = false;
438 if (_M_has_sol)
439 {
440 if (_M_nfa._M_flags & regex_constants::ECMAScript)
441 _M_results = _M_cur_results;
442 else // POSIX
443 {
444 __glibcxx_assert(_M_states._M_get_sol_pos());
445 // Here's POSIX's logic: match the longest one. However
446 // we never know which one (lhs or rhs of "|") is longer
447 // unless we try both of them and compare the results.
448 // The member variable _M_sol_pos records the end
449 // position of the last successful match. It's better
450 // to be larger, because POSIX regex is always greedy.
451 // TODO: This could be slow.
452 if (*_M_states._M_get_sol_pos() == _BiIter()
453 || std::distance(_M_begin,
454 *_M_states._M_get_sol_pos())
455 < std::distance(_M_begin, _M_current))
456 {
457 *_M_states._M_get_sol_pos() = _M_current;
458 _M_results = _M_cur_results;
459 }
460 }
461 }
462 }
463 else
464 {
465 if (_M_current == _M_begin
466 && (_M_flags & regex_constants::match_not_null))
467 return;
468 if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
469 if (!_M_has_sol)
470 {
471 _M_has_sol = true;
472 _M_results = _M_cur_results;
473 }
474 }
475 }
476
477 template<typename _BiIter, typename _Alloc, typename _TraitsT,
478 bool __dfs_mode>
479 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
480 _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i)
481 {
482 const auto& __state = _M_nfa[__i];
483
484 if (_M_nfa._M_flags & regex_constants::ECMAScript)
485 {
486 // TODO: Fix BFS support. It is wrong.
487 _M_dfs(__match_mode, __state._M_alt);
488 // Pick lhs if it matches. Only try rhs if it doesn't.
489 if (!_M_has_sol)
490 _M_dfs(__match_mode, __state._M_next);
491 }
492 else
493 {
494 // Try both and compare the result.
495 // See "case _S_opcode_accept:" handling above.
496 _M_dfs(__match_mode, __state._M_alt);
497 auto __has_sol = _M_has_sol;
498 _M_has_sol = false;
499 _M_dfs(__match_mode, __state._M_next);
500 _M_has_sol |= __has_sol;
501 }
502 }
503
504 template<typename _BiIter, typename _Alloc, typename _TraitsT,
505 bool __dfs_mode>
506 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
507 _M_dfs(_Match_mode __match_mode, _StateIdT __i)
508 {
509 if (_M_states._M_visited(__i))
510 return;
511
512 switch (_M_nfa[__i]._M_opcode())
513 {
514 case _S_opcode_repeat:
515 _M_handle_repeat(__match_mode, __i); break;
516 case _S_opcode_subexpr_begin:
517 _M_handle_subexpr_begin(__match_mode, __i); break;
518 case _S_opcode_subexpr_end:
519 _M_handle_subexpr_end(__match_mode, __i); break;
520 case _S_opcode_line_begin_assertion:
521 _M_handle_line_begin_assertion(__match_mode, __i); break;
522 case _S_opcode_line_end_assertion:
523 _M_handle_line_end_assertion(__match_mode, __i); break;
524 case _S_opcode_word_boundary:
525 _M_handle_word_boundary(__match_mode, __i); break;
526 case _S_opcode_subexpr_lookahead:
527 _M_handle_subexpr_lookahead(__match_mode, __i); break;
528 case _S_opcode_match:
529 _M_handle_match(__match_mode, __i); break;
530 case _S_opcode_backref:
531 _M_handle_backref(__match_mode, __i); break;
532 case _S_opcode_accept:
533 _M_handle_accept(__match_mode, __i); break;
534 case _S_opcode_alternative:
535 _M_handle_alternative(__match_mode, __i); break;
536 default:
537 __glibcxx_assert(false);
538 }
539 }
540
541 // Return whether now is at some word boundary.
542 template<typename _BiIter, typename _Alloc, typename _TraitsT,
543 bool __dfs_mode>
544 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
545 _M_word_boundary() const
546 {
547 if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow))
548 return false;
549 if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow))
550 return false;
551
552 bool __left_is_word = false;
553 if (_M_current != _M_begin
554 || (_M_flags & regex_constants::match_prev_avail))
555 {
556 auto __prev = _M_current;
557 if (_M_is_word(*std::prev(__prev)))
558 __left_is_word = true;
559 }
560 bool __right_is_word =
561 _M_current != _M_end && _M_is_word(*_M_current);
562
563 return __left_is_word != __right_is_word;
564 }
565} // namespace __detail
566
567_GLIBCXX_END_NAMESPACE_VERSION
568} // namespace
569